Oil sludge is one of the major solid wastes generated during oil field exploration, transportation, and petroleum refineries, which can cause severe soil, water, and air pollution. Pyrolysis is an effective technique for reducing oil sludge and achieving energy reutilization. Herein, the thermal characteristic mechanism and precipitation characteristics of oil sludge were studied using thermogravimetric Fourier transform infrared (TG-FTIR) analysis. Results show that the oil sludge pyrolysis process can be divided into three stages, namely, the release of water and a part of the light fraction, the release of organic materials, and the decomposition of carbonate compounds. The increase in the heating rate, affected by the delay in the internal heat and the mass transfer of oil sludge, led to the shift of the TG and derivative thermogravimetry (DTG) curves of the overall pyrolysis weight loss toward the high-temperature zone. Moreover, the pyrolysis process released CH₄, CO, CO₂, and volatile substances such as alkane, olefin, and aromatic hydrocarbons.